Browsing by Author "Rodrigo, WDAS"

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item: Thesis-Full-text
Analyzing power quality issues of wind power plants in puttalam
(2015-11-27) Dissanayake, DMMT; Rodrigo, WDAS; Wijekoon, HM
Wind Power development has become a booming industry due to its advantages over conventional thermal power sources. However, wind is considered as an intermittent source in terms of power quality as wind turbines have an uneven power generation following natural variations of wind. Power quality (PQ) is an important issue for electricity consumers at all levels of usage, particularly industrial sector as PQ disturbances ultimately lead to huge economic losses and safety concerns. The research objectives are; to study on major power quality issues associated with four wind plants in Puttalam, propose suitable PQ improving methods and to identify the most suitable wind technology in view of power quality. Project scope includes measurement of electrical parameters at each plant, analysis of parameters based on “IEC 61400-21” and “Grid Connection Requirement” published by Ceylon Electricity Board, study on mitigation techniques, computer modeling and simulation in MATLAB/SIMULINK environment to investigate harmonic mitigation. For each power quality aspect, a set of norms and marginal values were set to evaluate each wind plant’s performance. There are four distinct wind technologies and three of them are available in Sri Lanka. Out of these technologies, Wind Turbine type “C” which employs a Doubly-Fed Induction Generator with a partial scale power converter shows the best power quality characteristics. From Measurements and Data Analysis it was concluded that, none of the investigated plants adhere to power quality requirements of the grid code. Neither the utility (CEB) nor the Wind Power Producers pay adequate attention on these violations. It is recommended to pay more attention on PQ deviations. Systems must be developed to continuously monitor PQ parameters and take necessary actions to keep them within specified levels. Further, hybrid filters to reduce harmonic distortion and Dynamic Voltage Restorers to mitigate voltage sags are proposed for WPPs under study.
item: Thesis-Full-text
Assessment of cost of externalities for CEB thermal generation options
Karunaratne, SAPU; Rodrigo, WDAS
Costs of externality are effects that are typically not taken into account in finalizing the market price of goods or materials. Environmental impacts and social damage costs are the main externalities needed to be considered.There is a growing requirement for policy analysts to take account of the environment in their decision making and to undertartake the specified cost benefit analysis. Therefore it is a vital fact to monetary value the social and environmental damage that can be occurred due to an infrastructure and to use it as a variable cost. In the case of power generation, electricity production causes environmental damages of which the associated costs are not borne by the producers or consumers of that electricity. Hence, true generation costs should include both the private costs incurred to provide power such as capital cost, O&M cost and labour and the external costs of damage to the environment. In Sri Lanka, due to the absence of reliable health and environmental impact studies, an estimated value of 0.13 US Cents/kWh was added as the social damage cost for the scenario studies of coal in Long Term Generation Expansion Plan, (2012 -2032) by the Generation Planning unit of Ceylon Electricity Board. Thus, in this research, a realistic monetary value for the social damage cost is assessed for coal power generation studies in Sri Lanka based on the environmental and social impacts associates with it. The Impact path way method is discussed and used for the monetary valuation. The respective pollution levels are obtained by means of Gaussian plume air dispersion model. Then with certain assumptions and limitations, value of 0.08 US Cents/kWh is derived as the external cost or the social damage cost for coal power generation studies .Finally, conclusions are drawn based on results and sensitivity analyses
item: Thesis-Full-text
Automated demand response for a commercial building : a model design and pilot study
Fernando, CTJ; De Silva, PSN; Rodrigo, WDAS
The inherent intermittency of non-conventional renewable resources has been the major impediment in admitting renewable resources to the traditional Electricity Grid. The flexibility of loads in the power system are disregarded in such analysis. The traditional Utility and Customer model is now subjected to change with active customer participation from demand side. With the growing renewable share in the Energy mix, power industry will require more capacity and inertia to have a better control over the power quality. Automated Demand Response is the cutting edge technology which enables the grid to use load flexibility in counteracting the NCRE intermittency. This project pilots the possibility of mitigating the rooftop solar intermittency of a building with air conditioning loads which has an inherent flexibility as DR resources. A building-wide Home Area Network is implemented together with short term solar prediction and a central controller with dynamic dispatch algorithm. esults from the pilot project are presented to demonstrate as how the solar transients are mitigated at the Point of Common Coupling (PCC) with an eye on benefits and impacts on the participants.
item: Thesis-Full-text
Autonomous fault isolation and power restoration system for MV/LV distribution
Dissanayaka, DMDK; Rodrigo, WDAS; Hemapala, KTMU
The term “Distribution Automation” generally refers to a distribution network switching subsystem devices equipped with the advanced technologies dedicated for purposes such as, ease of real time monitoring and controlling, reliability improvement management, integrating of distribution network and electricity market operation. Improving the reliability of electric power delivered to the end users is one of the main targets of employing distribution automation. Therefore, developing autonomous fault isolation and power restoration system for LV/MV distribution can be attractive reliability enhancement solution for the electric utilities. Electrical utility industries are not focusing on automating Low Voltage (LV) distribution system due to complexity of the LV distribution network feeders. However, there is a room available for automation if an algorithm could be developed for autonomous fault isolation and power restoration. Development of a comprehensive algorithm opens up a new pathway for LV distribution. Electrical distribution system network consists in large numbers of Remote Switching Subsystem Devices (RSSD) and these devices communicate in different protocol. These devices can be monitored and controlled remotely by linking with Supervisory Control and Data Acquisition (SCADA) system. However, investing on a fully fledge SCADA is not so economical for a small scale distribution utility. As a solution; scalable distribution automation will enable small scale distribution utilities to enter into distribution automation with optimal capital investment. Hence, developing a scalable SCADA is the solution for smaller distribution automation. Results of this thesis are, a proto type LV distribution system has been developed to demonstrate the algorithm for autonomous fault isolation and power restoration system. Also has been implemented open platform SCADA system in view of acquiring multi-protocol remote switching subsystem devices.
item: Conference-Abstract
Cloud images capturing system for solar power level prediction
Rodrigo, WDAS; Perera, KHE; Priyadharshana, HMS; Priyanka, VGC; Ranasinghe, RARA
Solar energy has received increasing attention as one of the potential renewable energy sources for power generation in recent past. Introduction of Net Metering and the increment in provision for renewables encouraged the usage of Solar PV systems in Sri Lanka. However, the intermittent nature of solar energy has become one of the barriers for solar energy based power to be integrated to the national power grids. Due to unpredictability solar energy based power plants are non-dispatchable and can cause network instability. With an efficient and reasonably accurate predictable model, a better system balance can be achieved. Shadowing on solar PV modules results in reduction of power produced. Cloud coverage blocking the sun can be identified as the major contributor in shadowing. Identifying and tracking the clouds can be used to finally predict the solar PV output. This paper presents a methodology to obtain cloud image data and an algorithm to process the images which can be used to predict the relationship between the cloud movements and the solar PV output.
item: Thesis-Full-text
Condition monitoring and assessment of power transformers using sweep frequency response analysis and dissolve gas analysis.
Fernando, MPM; Lucas, JR; Rodrigo, WDAS
Power transformer can be considered as the key element in an electricity power system. Cost and the time of installation of a power transformer are significantly higher than the installation of other equipment. Applied electrical and thermal stresses due to various factors always deteriorate the condition of transformers. In this sense, it is important to monitor and assess the condition of Power Transformers to ensure longer operation as well as to maintain a reliable operation of a power system. Sweep Frequency Response Analysis (SFRA) can be used to assess the mechanical integrity of transformers. The test measures the transfer function response of the active part of the transformer. The three frequency responses of three phases should be identical except to inherited variations, and therefore, it can be considered as a fingerprint for a transformer. If any physical changes occur within and between the elements of the transformer, it will affect the frequency response, which can be used to detect any abnormality. However, correct interpretation of the measured response in determining the transformer condition is a critical challenge, as interpretation of frequency response is still not fully established. On the other hand, Dissolve Gas Analysis (DGA) can be used to assess the possible stresses that could have been applied on the oil immersed transformers based on the concentration of specific gases dissolved in oil. Several diagnosis tools recommended by international standards are available and they have been using by utilities over a period of time with reasonable reliability. In this study, SFRA and DGA measurement data were collected from set of power transformers in operation, and analyzed those approaching to develop a methodology to assess the condition of power transformers, correlating outcomes from SFRA and DGA. For this, transformers taken for the study were categorized based on their SFRA data by analyzing behavior of the response of the three phases and their Page | iv similarity. Several indices were introduced to quantify the similarity. In the other hand, the selected transformers were categorized based on their DGA data considering the recommendations provided by available standards and diagnosis tools. Further, a Computing Tool was developed using MATLAB, for the easy evaluation of the SFRA and DGA measurements. Finally, several case studies were carried out justifying the proposed methodology verifying the benchmarking of the introduced indices against several faulty and good transformers.
item: Thesis-Full-text
Condition monitoring of metal oxide surge arresters at power distribution
Arshad, SM; Rodrigo, WDAS
Metal Oxide Surge Arresters (MOSA) are proven to be reliable protective devices for power distribution and electrical transmission system. MOSA are subjected to electrical ageing or degradation due to constant AC conduction or transient voltages. Leakage current measured from surge arresters are used to observe its degradation and the resistive leakage component is extracted from the total to determine the health of the surge arresters. If resistive current increases, life of the surge arresters decreases. Generally leakage current is measured using current shunts or current transformers where it’s necessary to measure the applied voltage which is very hard to measure in online condition. This proposed study develops a simple but accurate method to separate the resistive leakage current from the total leakage current without any voltage measurements by using a technique called Modified Phase Shifted Method (MPSM) which is totally based on manipulation of the total leakage current waveform and simulated in Matlab & Simulink. A prototype device is designed and developed to sense the leakage current from a surge arrester and transmit those data to Matlab & Simulink to perform the MPSM and determine the its resistive leakage current. This method enables remote and an online monitoring system which can alert the utility whenever the health of the installed surge arrester becomes low.
item: Thesis-Full-text
Cost optimal surge protective system for low voltage installations
Dadallage, KK; Rodrigo, WDAS
Surge protective devices (SPDs) have become an integral part of residential, commercial and industrial power quality applications. A wide selection of surge SPDs are promoted by greater number of manufactures for the protection of electrical and electronic systems damaging effects of electrical transients and lightning. The selection of the appropriate cost effective SPD is great difficult due to some manufactures use different technologies and many manufactures specify their SPD performance differently. One of the difficult tasks encountered when specifying a SPD is identifying and understanding the ratings associated with its application. There are many performance values and ratings associated with an SPD, such as Maximum Continuous Operating Voltage (MCOV), Voltage Protection Rating (VPR), Nominal Discharge Current (In), and Short Circuit Current Rating (SCCR). The most important and misunderstood rating is the Surge Current Rating. In today’s market there are numerous SPDs with surge current ratings ranging from 10 kA through 1000 kA with different prices. The research presents a methodology to select cost optimal surge protection devices for low voltage installations. The procedure for the selection of SPD is considered the steps of risk assessment, IES standard, manufacture technical details, the applied technology and the data bank of SPD available in local market. The cost optimal solution has been obtained by user friendly software considering the risk assessment result, area lightning density, location and the geographical factors.
item: Thesis-Full-text
Designing earthing system for distribution transformers in high resistive soils at restricted areas
(2015-10-30) Fernando, AHGR; Rodrigo, WDAS
Earthing of Distribution Transformer is very important in the sense of safety and protection of human beings, livestock and equipment. The construction personals have faced critical issues on earthing when they engage in Installations of Electrical equipment due to high values of earth resistance. The research was carried out to find solutions for two objectives. One of objectives is to design an earthing system for high resistive soil. The other objective is to find solution for earthing in restricted area. It was found that high resistive soil exists in sandy soils in coastal areas as well as hard rocky areas in central part of the Island. There are some rocks located in coastal area too. The soil resistivity plays vital role in earthing of electrical installations. Thus the research was done by using soil enhancement materials such as Charcoal, Lime and Sand of the same location. The mixture of above materials improves the electrolytic property of soil to bring down soil resistivity. The research was done in the field and at laboratory by varying the ratios of Charcoal, Lime and Sand. The test results showed that resistivity becomes minimum value, when the ratio becomes 1:1:3.of Charcoal: Lime and Sand respectively. The usage of optimum land area for earthing of distribution transformers were achieved by using the base of poles of transformer structure as alternative earth pits. A new design for earth mesh for pole base earth pits was introduced as a result of the research. An economic analysis was carried out to find the benefits of using soil enhancement materials instead of cement block earths. As a result of eliminating cement block earth, there is a financial gain of 18.39%. The case studies were carried in Chilaw area for two different soil types by mixing soil enhancement materials. In this study moisture content of the soil was measured to identify the effect of presence of moisture in soil. The results of the research indicated that the earth resistance drastically reduces due to the presence of moisture content and the organic substances of the soil in addition to the soil enhancement material. Finally, the Ansys-Maxwell software was used for simulate the earthing system in homogeneous medium. The results of simulation were shown that major portion of the energy absorbed by the narrow region, very close to the earth rod. Therefore, the diameter of the earth pit can be reduced to minimize the area of land required for earthing of distribution transformers. It shows the voltage distribution and energy dissipation in the critical cylinder very clearly. In this research a new conceptual design was carried out to reduce earth resistance in newly designed earthing system and in existing transformers by increasing the moisture content around the earth rods of earth pits. An external water container is introduced toprovide water drops to earth pit to keep it at wet condition in dry season to improve the efficiency and effectiveness of the earthing system.
item: Thesis-Full-text
Determination of maximum possible loading capacity of a single generator unit : a case study for the present Sri Lankan power system
Ranjitha, RS; Rodrigo, WDAS
Present Sri Lankan power system consists of a rich energy mix and a vast diversity within all over the island, out of which hydro power generation is predominant. Even though hydro power generation is predominant and has least operational cost, the emerging consumer demand growth cannot be catered by hydro power generation only. In addition to hydro power, nearly 50% of country’s energy demand is fulfilled by three number of coal power plants which are considered as largest capacity low cost thermal power plants in the country and are operated in base load basis. Even though these large scale coal power plants are very much cost effective and have large net output power capacity, considering the system reliability, they cannot be dispatched in full load manner during certain demand conditions and different dispatch conditions which are currently practiced by Ceylon Electricity Board, which is the country’s main power utility which has the authority to large scale electricity generation, transmission and distribution. The reason is when such a large generator gets tripped, the frequency stability and voltage stability would be highly vulnerable for resulting the system collapsing due to such large generation rejection from the system. Recently the national power network has experienced several failures due to tripping of such large generators during certain demand condition under different dispatch conditions. Hence, it has become a challenging decision to determine the loading capacity of the large generators when it comes to system operations. A model has been implemented with PSS/E software and has been validated with actual system incidents considering latest power system parameters. This validated model has been used for simulating generation rejections according to the appropriate generation percentages during all the dispatch scenarios considering worst case demand conditions. This study evaluates the capacity percentage range of the maximum loading capacity of single generator unit considering both frequency stability and voltage stability, compromising both power system operational cost and power system reliability as a case study which is carried out considering the parameters of operational guide lines of present Sri Lankan national power system.
item: Thesis-Full-text
Develop an effective methodology to evaluate the energy loss in low voltage network
Weththasinghe, TN; Rodrigo, WDAS
Power system losses have turned out to be a major challenge for electricity utilities worldwide and losses in electricity distribution represent dominant part in the overall power system losses. In the Sri Lankan context, losses in the distribution system are around 8.5% of gross electricity generation when the total losses in transmission and distribution amount to 10.5% in 2014. Though this can be viewed as a reasonably good level, when compared with the power system losses in rest of the developing countries in the region, country need long strides to reach the levels achieved by the developed countries. Before formulating strategies for loss reduction, it is essential to determine the losses at each level. Once losses are segregated, utility can clearly identify their priorities and launch effective programs to arrest losses. At present the CEB doesn’t have the data required to calculate the energy loss of the LV network and has only few basic information. Further collecting LV network data and calculating the LV loss by modeling the LV network is difficult to be done practically. So, the objective of this study was to build a suitable methodology to calculate the transformer wise energy loss using the available LV network data in CEB to identify the transformers with high technical energy loss and the areas with higher nontechnical loss. In this study, total transformers were divided into 3 groups according to the consumer mix and 6 sample transformers were selected. Then calculated the technical power loss of feeders after doing the synergy modeling for the each feeder that has been selected and a formula was built to calculate the feeder power loss based on the results obtained. The technical energy loss of each transformer is calculated after calculating the feeder wise technical power loss of the 20 transformers using the built formula. Based on the results of the 20 transformers a formula was built to calculate the technical energy loss. According to the results of this study, the technical energy loss of LV network in Ratmalana area is 2.6%. and it increases to 3.12%, when lines are consisted with 70 mm2 ABC lines. Further, there are 10% of transformers in this area with technical energy loss greater than 4% and 50% of the transformers has a value less than 1.5%.
item: Article-Abstract
Developing a test bench to test grid tie inverters
Gunarathna, PYTD; Rodrigo, WDAS; Arachchi, TML; Weerarathna, HD; Wickramanayake, CK
The need of electricity through-out the world is growing day by day at a considerable rate. The electricity demand of its consumers has already exceeded the supply. Hence, switching towards green energy is a must to remove this imbalance conditions between the electricity supply and demand. At this particular point, there is a higher tendency of the electricity consumers for moving towards domestic solar power. The grid tie inverters are the main building. So, the proper operation of an inverter is highly important. Although there exists an already provided data sheet by the manufactures along with the inverters, sometimes we can identify mal-operation conditions of these inverters irrespective of the data sheet provided and therefore, many complaints are aroused by the solar consumers. The issue is that there does not exist proper equipment to engage with all types of inverter testing schemes that had been listed in the IEEE 1547 standard; which is the relevant safety standard for interconnecting distributed resources with electric power systems. So, a test bench to test the grid tie inverters was developed according to IEEE 1547 standard. Tests that are stated in the standard were conducted with a higher accuracy data acquisition system and the relevant results were analyzed to determine whether a particular inverter operates within the limits at abnormal situations as described in the standard. Finally, a test report was generated to provide the solar power consumer informing the operation status of the inverter. This paper elucidates relevant inverter tests, the proposed methodologies to conduct the tests, the logic behind those tests for analysing purposes and the test results obtained for the calculations of the necessary test parameters, thus, the entire outcome will be highly important for the industry.
item: Thesis-Full-text
Distribution loss reduction through energy management for rural electrification
Gunasekara, JN; Wijekoon, HM; Rodrigo, WDAS
The Ministry of Power & Energy has taken initiative to electrify rural areas to uplift the living standard of the people in rural areas by providing the electricity, which is a basic need of people. Ceylon Electricity Board gives special concessions to in line with this by initiating number of rural electrification Projects Island wide. This increases the distribution losses by increasing the line lengths and by adding number of under loaded transformers to the power system. In this study, three main factors; selection of proper transformer capacity, effect of high tension line reconductoring, and effect of reactive power compensation are discussed in concerned to reduce the line losses in rural areas. The analysis was done as a case study for the Monaragala consumer service area. It was required to initially determine the load growth rate and the load factor for the area of concern. Load factor was obtained from the daily load curve of the passara feeder which feeds to the Monaragalaarea. The tabulated value was 0.395. The load growth rate of the area was analyzed by collecting the historical data of 167 numbers of identified transformers located in three consumer centers in the Monaragala area from year 2010. The resulted load growth rate of 0.48 was used in the analysis for data forecasting for next twenty years. The total cost of a transformer includes the initial purchase costs, maintenance cost and the cost due to losses of the transformer throughout the lifetime. The cost due to losses will be a cost for the country as a whole since this will affect to the total generation capacity to meet the country’s demand. Therefore the proper selection of transformers is vital for any electrical installation. Transformer losses were forecasted for next twenty years, for different transformer capacity ratings and total costs were analyzed. If the initial peak load of the transformer is less than 30 kVA, the most economical transformer is 63 kVA. In rural distribution systems, its large number of low load consumers is distributed over a large geographical area lengthening the network and this has created more problems to the energy management. The results of the case study done for the Monaragala area clearly shows that the HT reconductoing is not economically viable, with respect to the line loss reduction in the RE network is very low. This study is focused to analyze the effect of loss reduction by reactive power compensation too. The results of this case study for Monaragala area shows that it is more feasible to install a one 1200 kvar fixed type capacitor for Passara feeder of the Badulla Grid Substation (GSS). More generalizing the outcome of this research, it can be concluded that for rural areas, which are having the load growth rate around 40% or below than that capacitor installation is economically viable and the ratings to be determined by a cost benefit analysis.
item: Thesis-Abstract
An Effective methods of segregation of losses in distribution systems
(2015-06-30) Gunathilaka, MDPR; Rodrigo, WDAS; Siyambalapitiya, T
Power system losses have turned out to be a major challenge for electricity utilities worldwide. Bulk of the losses occurs in electricity distribution. In 2012, the overall energy loss and the distribution system loss in the Sri Lanka power system were about 14% and 10% of the gross generation respectively. Before formulating strategies for loss reduction, it is essential to determine the losses at each level. Once losses are segregated, utility can clearly identify their priorities and launch effective programmes to arrest losses.The objective of this research study is to segregate losses in a selected area of the distribution system of Ceylon Electricity Board, and evaluate an advanced metering solution in view of reduction of losses. Western Province North of which the distribution network spreads in the entire Gampaha district, Sri Lanka, was selected for the study. Accordingly, the losses were segregated into medium voltage network loss, losses in distribution transformers and low voltage network loss. The total energy loss in the distribution system was 7.1% of the energy input to the system in 2012. The loss in the low voltage network was 5.1 % of the total energy input. However, it was 15.7% of the energy input to the low voltage network itself. A study was also carried out to determine losses in the low voltage networks of two distribution substations. The technical losses were estimated and thereby the non-technical losses were derived. The total losses were 13.9% and 8.8% of the respective energy input to the low voltage networks of the two substations. The technical losses were 5.1% and 4.8% while non-technical losses were 8.9% and 3.9% respectively. The viability of an advanced metering solution was assessed based on the same low voltage networks. Deployment of advanced metering systems solely with the purpose of arresting non-technical losses is not viable. However, viability of full scale deployment of advanced metering shall be studied at broader level considering any future requirements for time of use metering, avenues for demand side management, opportunity to reduce system peak through demand response principles, possible levels of reduction of losses and other benefits to utility and country as a whole. Key words – Technical Loss, Non-technical loss, Load factor, Load loss factor, Advanced metering
item: Conference-Abstract
Fault management algorithm for voltage feeder automation in electricity distribution
Dissanayaka, DMDK; Hemapala, KTMU; Rodrigo, WDAS
The term Distribution Automation (DA) generally refers to a distribution network which is equipped with the advanced technologies dedicated for purposes such as, ease of real time monitoring and controlling, reliability improvement management, integrating of distribution network and electricity market operation. Improving the reliability of electric power delivered to the end users is one of the main targets of employing distribution automation. Therefore, developing autonomous fault isolation and power restoration system for Low Voltage (LV) distribution can be an attractive reliability enhancement solution for the electric utilities. Manual operated LV distribution network has several activities in fault management. Most of the activities are unwanted time consuming activities due to the lack of automation in the LV distribution network. Time duration for fault management activities in manual operation has been measured in order to validate the proposed automation system. Electrical utility industries are not focusing on automating LV distribution system due to the complexity of the LV distribution network feeders. A low cost and simple system has introduced by the authors as the first step. A new algorithm for fault detection, isolation and power restoration to the healthy section was introduced. Initial step of the algorithm is to separate the faulty section which is occurred either sides of the adjoining switch. Second part is the faulty section finding algorithm. Third step is power restoration algorithm for faultless section and at the end reset the system. The proposed algorithm is an open algorithm and hence electric utilities can be used it for LV feeder automation easily. Accuracy of the proposed algorithm was checked with the developed prototype system.
item: Thesis-Full-text
Feasibility of scheduled running of existing mini hydro power plants
Hettiarachchi, YSK; Rodrigo, WDAS
The Electricity system load profile of Sri Lanka has a high evening peak demand and as a result has a low load factor. The load curve has a close relationship with the human behavior and other economic activities of the country, having a morning peak, Day peak and a night peak. Even though it is desirable to have a flat load curve, due to this behavioral impact, the curve is having rather large variations. The extent of variation is so substantial that the maximum demand is having a greater value, which is about 2.24 times of the minimum demand. During the dry season water level of the large hydro reservoirs is getting decrease rapidly and system demand fulfill by thermal generation of CEB and Private Power Plants. Therefore most of the high cost small thermal generators should be operated in the evening peak hours. Hence, CEB has to pay additional cost for power generation than income earns from electricity selling to the customer. That reason is happened to fulfill the peak demand using high cost thermal generation. The objective ofthis feasibility study is prepared the system ofscheduled running for existing mini hydro power plants to reduce high cost thermal generation at evening peak hours. The study has contained the energy mix of Sri Lanka, behavior of thermal generation in future, present mini hydro running pattern, possibility of schedule running of existing mini hydro plants and prepare the generalized system to operate mini hydro plant for schedule running. According to the results, some of mini hydro plants in the existing system can operate under the scheduled running and the results of scheduled mini hydro plants have affect to reduce high cost thermal generation by small thermal generators.
item: Thesis-Abstract
Feasible study on the power quality issues of voltage variation and harmonics due to PV penetration in LVDN : a case study in Negombo LVDN Sri Lanka
(2024) Saravanapavan, S; Rodrigo, WDAS
Renewable energy resources are encouraged all over the world to have a green power generation to avoid global warming due to conventional energy sources. As one of a sustainable power source, solar photovoltaic system is considered in micro grid and domestic solar system. Domestic solar systems have a rapid growth in Sri Lanka since last decade and they are connected with the existing low voltage distribution network. Therefore, it causes power quality issues with increasing PV penetration in LVDN. The common PQ issue arising from PV penetration is the voltage rise. Therefore, a LVDN with voltage rise issue in Negombo, Sri Lanka was selected for the case study of this research. This research focused on a LVDN with low active power existence and high feeder resistance where the voltage rise is due to feeder resistance with increasing PV penetration. This study considered power quality issues of voltage violation, harmonic analysis and power factor violation in the selected LVDN. Analysis of another LVDN with different transformer capacity was also summarized in this study. The mitigation techniques of active network management and network reinforcement were applied to the LVDN and the response was analyzed. The harmonic results were insignificant with voltage violation. And when the voltage rise was mitigated with tap settings, the harmonic results were more insignificant compared to the previous. Therefore, harmonic analysis was not carried out for further analysis. The enhancement of hosting capacity with different mitigation techniques was analyzed while considering voltage violation and power factor violation. The mitigation technique of active network management with balancing loads, tap settings and increasing the loading of the network, increased the hosting capacity from 50kW (31% w.r.t t/f capacity) to 108kW (68%) at no cost. Reactive power compensation schemes did not provide solution as it violates the power factor of the network while mitigating the voltage variation and vice versa. Because, the required reactive power to mitigate the voltage rise becomes significant compared to the active power existence in the network. Mitigation technique of energy storage system also did not provide solution for the low load demand LVDN. The mitigation techniques of network reinforcement methods were applied. It increased the hosting capacity up to 144kW (90%) with upgrading conductor, 153kW (96%) with the installation of OLTC with AVR and the installation of separate PV feeder did not increase the hosting capacity. The cost estimation was done for the mitigation techniques. And it is concluded that the techno economic feasible solution as upgrading conductor with 95sqmm conductor size is selected as the mitigation technique for this existing system. The conclusions of this study are as follow. The network reinforcement mitigation techniques are more suitable than the reactive power compensation schemes, for a PV penetrated LVDN with low active power existence and high feeder resistance, in order to increase the PV penetration, when the voltage rise is due to the feeder resistance. Reactive power compensation methods are suitable for the network with high active power existence and/or high reactive power existence, otherwise it would violate the power factor and/or voltage. Installation of solar PV system in the LVDN will make the system better, to overcome from the effect of the high feeder resistance and it will increase the loading capability of the network while maintaining PQ standards. The increase in the day time loading of the network, increases the PV penetration. Mitigation techniques of active network management of balancing loads and tap settings also increases PV penetration at no cost in such LVDN. Feeder resistance and loading of the network give more impact in deciding the hosting capacity of such LVDN. Therefore, the network reinforcement techniques are more suitable for LVDN with low active power existence and high feeder resistance. Future analysis can be extended for a small scale LVDN with PV systems including significant nonlinear loads and reactive loads.
item: Thesis-Full-text
Impact of high penetration of solar PVS on harmonics in LV distribution networks
(2018) Anurangi, RO; Rodrigo, WDAS; Jayatunga, U
Present trend of using solar photovoltaic (PV) technology for generating electricity has marked a rapid growth in the number of grid connected solar PV systems which has been reported to make a considerable impact on the power quality in the grid. With comparison of power quality (PQ) problems such as voltage unbalance, local voltage rise and voltage fluctuations, the increase of network harmonic levels has been identified as a potential PQ concern with the grid connected solar PVs. PV inverters are source of harmonics that produces low order and high order harmonics at the switching frequency and its side bands. Low order harmonics present at the inverter output due to the inability of producing pure sinusoidal waveform. Varying solar irradiance, inverter characteristics, inverter capacity, multi-inverter interactions and background harmonic level are examples of factors which influence the amount of harmonic generation of a PV system. This research focuses on the effect of high levels of harmonic injection and propagation of current harmonics in distribution network with solar PV integrations. A methodology is discussed in this thesis to achieve the aforementioned matter with the detailed modeling of PV inverters in a typical distribution network using PSCAD/EMTDC simulation platform. From the analysis of simulation results, the current harmonics injected by single phase inverters has been found substantial and influential with regard to the energy transmission and increase losses with compared to the three phase inverters. Unbalance occurred due to single phase inverters results in triplen harmonics to propagate to the upstream grid via the distribution transformer. Moreover, current harmonics superimposition were recorded as a result of multi-inverter operation. It was found that the Point of connection (POC) of the PV inverter affects the voltage harmonic levels at the inverter output.
item: Article-Abstract
A Model for the perception of surface pressure on human foot
Xiong, S; Goonetilleke, RS; Rodrigo, WDAS; Zhao, J
The psychophysical relationship between the magnitude of pressure on thirteen test locations of twenty healthy subjects’ feet with four probe areas at three indentation speeds and the corresponding perceived sensations were analyzed. The dependency of pressure pain thresholds (PPT) on area, A, and speed, v, can be mathematically modeled in the form, PPTi ¼ [ai þ bLn(v)]Ab i ¼ 1,2.13 where b and b are constants and are dependent on location and gender, and ai is a constant highly correlated with foot tissue stiffness. The relationship between the sensory intensity to pressure magnitude appears to follow a modified Stevens’ power law with power exponents less than 1.0 and consistent across the 13 test locations with a mean of 0.82 and a range from 0.67 to 0.98. This particular model helps to understand the sensation of pressure threshold and its impact in the design of consumer products.
item: Conference-Abstract
Modeling and simulation of current source converter for proposed India-Sri Lanka HVDC interconnection
Rodrigo, WDAS; Perera, CU
The proposed 500 MW interconnection is the first DC power transmission link that is planning to connect in between Sri Lankan and Indian AC transmission networks. Proposed AC-DC system integration should determine the asymptotic stability of transmission network in both countries. Reliability can be improved by properly selecting system configurations. Properly selected DC & AC system parameters determine the stable performance at steady state and at perturbed conditions. This paper presents the modelling analysis of proposed HVDC interconnection for selected physical configurations. The interconnection was modelled using PSCAD/EMTDC software and simulated under the steady state conditions and perturbed conditions. The analytical results were verified using time domain simulations.